DESCRIPTION

In many applications it's wise to let Perl use Unicode for the strings it processes. Most of the interfaces Perl has to the outside world are still byte based. Programs therefore need to decode byte strings that enter the program from the outside and encode them again on the way out.

The POSIX locale system is used to specify both the language conventions requested by the user and the preferred character set to consume and output. The Encode::Locale module looks up the charset and encoding (called a CODESET in the locale jargon) and arranges for the Encode module to know this encoding under the name "locale". It means bytes obtained from the environment can be converted to Unicode strings by calling Encode::encode(locale => $bytes) and converted back again with Encode::decode(locale => $string).

Where file systems interfaces pass file names in and out of the program we also need care. The trend is for operating systems to use a fixed file encoding that don't actually depend on the locale; and this module determines the most appropriate encoding for file names. The Encode module will know this encoding under the name "locale_fs". For traditional Unix systems this will be an alias to the same encoding as "locale".

For programs running in a terminal window (called a "Console" on some systems) the "locale" encoding is usually a good choice for what to expect as input and output. Some systems allows us to query the encoding set for the terminal and Encode::Locale will do that if available and make these encodings known under the Encode aliases "console_in" and "console_out". For systems where we can't determine the terminal encoding these will be aliased as the same encoding as "locale". The advice is to use "console_in" for input known to come from the terminal and "console_out" for output known to go from the terminal.

In addition to arranging for various Encode aliases the following functions and variables are provided:

decode_argv( )

decode_argv( Encode::FB_CROAK )

This will decode the command line arguments to perl (the @ARGV array) in-place.

The function will by default replace characters that can't be decoded by "\x{FFFD}", the Unicode replacement character.

Any argument provided is passed as CHECK to underlying Encode::decode() call. Pass the value Encode::FB_CROAK to have the decoding croak if not all the command line arguments can be decoded. See "Handling Malformed Data" in Encode for details on other options for CHECK.

env( $uni_key )

env( $uni_key => $uni_value )

Interface to get/set environment variables. Returns the current value as a Unicode string. The $uni_key and $uni_value arguments are expected to be Unicode strings as well. Passing undef as $uni_value deletes the environment variable named $uni_key.

The returned value will have the characters that can't be decoded replaced by "\x{FFFD}", the Unicode replacement character.

There is no interface to request alternative CHECK behavior as for decode_argv(). If you need that you need to call encode/decode yourself. For example:

Windows

Windows has basically 2 sets of APIs. A wide API (based on passing UTF-16 strings) and a byte based API based a character set called ANSI. The regular Perl interfaces to the OS currently only uses the ANSI APIs. Unfortunately ANSI is not a single character set.

The encoding that corresponds to ANSI varies between different editions of Windows. For many western editions of Windows ANSI corresponds to CP-1252 which is a character set similar to ISO-8859-1. Conceptually the ANSI character set is a similar concept to the POSIX locale CODESET so this module figures out what the ANSI code page is and make this available as $ENCODING_LOCALE and the "locale" Encoding alias.

Windows systems also operate with another byte based character set. It's called the OEM code page. This is the encoding that the Console takes as input and output. It's common for the OEM code page to differ from the ANSI code page.

Mac OS X

On Mac OS X the file system encoding is always UTF-8 while the locale can otherwise be set up as normal for POSIX systems.

File names on Mac OS X will at the OS-level be converted to NFD-form. A file created by passing a NFC-filename will come in NFD-form from readdir(). See Unicode::Normalize for details of NFD/NFC.

Actually, Apple does not follow the Unicode NFD standard since not all character ranges are decomposed. The claim is that this avoids problems with round trip conversions from old Mac text encodings. See Encode::UTF8Mac for details.

POSIX (Linux and other Unixes)

File systems might vary in what encoding is to be used for filenames. Since this module has no way to actually figure out what the is correct it goes with the best guess which is to assume filenames are encoding according to the current locale. Users are advised to always specify UTF-8 as the locale charset.